1. Field of the Invention
This invention relates generally to a beam monitoring assembly that monitors a laser beam for alignment and performance verification purposes and, more particularly, to a beam monitoring assembly that provides real time, non-intrusive monitoring of the near-field and far-field spacial mode and beam power of a laser beam using beam optics included in a laser head enclosure.
2. Discussion of the Related Art
High power, solid state lasers, such as diode slab lasers, that are used for many purposes, such as cutting, drilling and welding of various materials for precision laser machining (PLM), electronics manufacture, medical treatment, nuclear fusion, laser weapons, etc., are known in the art. A solid state slab laser will include one or more gain modules each having a solid state laser gain medium, such as a crystal of neodymium yttrium aluminum garnet (Nd:YAG), Yb:YAG, Ti: sapphire or neodymium glass (Nd:glass), and an optical pumping source to produce a population inversion in the gain medium. The gain medium typically has a slab configuration with a rectangular cross-section, an optically polished major side and end faces. The optical pumping source generally is one or more diode arrays positioned adjacent to the side faces of the slab. The laser gain medium absorbs light radiation from the diode arrays to create a population inversion within the medium to produce a laser beam output. The end faces of the slab are preferably formed at a non-perpendicular angle to the side faces so that light travels longitudinally in a zig-zag pattern through the laser gain medium as it is reflected off of the side faces. A high power solid state slab laser of this type is disclosed in U.S. Pat. No. 5,555,254 issued to Injeyan et al., Sep. 10, 1996, and U.S. Pat. application Ser. No. 08/683,585, filed Jul. 15, 1996, titled "Diode Laser Pumped Solid State Laser Gain Module", and assigned to the assignee of the instant invention.
The diode arrays are switched on and off or pumped in a controlled manner to generate a pulsed laser beam emitted from the gain medium that has a particular pulse rate and pulse width. The light output of the diode arrays can be accurately tuned to the absorption line of the active material of the laser gain medium to achieve a high pumping efficiency. An increase in the pulse rate and/or pulse width increases the power output of the laser beam. The diode arrays are fired in a controlled manner to set the pulse width and pulse rate of the output beam. The firing of the various diode arrays for multiple gain modules can be controlled independently of each other in sequence to further control the overall pulse width and rate for the laser beam, or generate a continuous wave (CW) beam. Therefore, depending on the particular application, the pulse rate and pulse width of the beam output is controlled for efficient laser operation for that application.
The type of solid state laser described above currently has a wide application in PLM. To perform a PLM operation, a laser operator will calibrate or program a controller that controls the laser to operate the laser beam at a desired power level and machining sequence to perform the desired machining operation. A single machining operation may include various degrees of cutting, welding, and drilling of a single workpiece or multiple workpieces. For example, the machining operation may require a welding operation and then immediately thereafter, drilling of a series of holes and/or cutting the workpiece. The welding operation generally requires different power levels than cutting and drilling operations, and the welding process itself may require different laser power levels. For example, welding around a corner of the workpiece may require a decrease in power because the welding operation may have to be slowed down and the resulting higher power may damage or burn the material of the workpiece at the slower speed. Further, the laser can be calibrated to weld a certain material, such as steel. If the operator then changes to a different material, such as a different steel, aluminum, copper, etc., different laser settings and output parameters would be required.
It is necessary to align the resonator cavity components of a laser for proper laser operation. To do this, a visual representation of the beam needs to be provided. Also, laser machines for PLM operations generally require a very bright and stable optical beam. It is therefore desirable to visually monitor beam quality and beam performance during a machining operation to maintain high precision machining. This image may also be used in an electronic image processing system that can actively control the alignment of the laser. It is important to verify the performance of the laser beam without interrupting the laser operation during material processing on factory floors, because the down-time of the laser system affects production schedules, and poor beam quality from varying output power effects product quality.
In order to provide beam alignment and monitor beam performance during a machining operation, it is beneficial to display the near-field and far-field images of the beam. The near-field image is the image of the beam as it leaves the laser, and the far-field image is the image of the beam at its focus, such as when it contacts the workpiece. In order to have a suitable beam performance for machining operations such as cutting and drilling, the near-field image of the beam needs to have a high degree of intensity and wave front uniformity, and the far-field image needs to have a high degree of beam circularity and intensity uniformity.
Optical systems are known for displaying the near-field and far-field images of a laser beam. However, these optical systems are typically large compared to the laser itself, and are not readily compatible to being combined with existing laser systems because of cost, complexity and size.
It is an object of the present invention to provide a beam monitoring assembly that provides beam alignment and performance capabilities by non-intrusive monitoring of the near-field spacial mode and the far-field spacial mode of a laser beam in a small compact package that can be readily positioned in a laser head enclosure.